The proposed research will amplify previous studies of enzymes involved in the metabolism of ornithine and glutamate in rat tissues during normal development. Experiments will test the way in which hormones promote functional differentiation by inducing or suppressing enzyme synthesis in different organs. An inbred strain with frequent mortality of the young and hormonally pretreated neonatal rats of another strain will be used as animal models to study aspects of the Sudden Infant Death Syndrome. In the newly proposed project ontogenic changes in arginase variants will be studied in liver, kidney and intestine of ammonotelic, ureotelic and uricotelic animals.